1. Field of the Invention
The present invention relates to an adhesive resin composition and a laminated material for which said adhesive resin composition is used, and more particularly an adhesive resin composition whose adhesivity is not impaired even in case it contacts with hot water, and a laminated material obtained by using said adhesive composition which has an excellent gas barrier property and is capable of withstanding treatment in retort.
2. Description of the Related Art
Polyester resins represented by polyethylene terephthalate resin are excellent in mechanical strength, rigidity, heat resistance, chemical resistance, oil resistance, and transparency, and have been extensively used as a packaging material, such as a film, sheet and container. The polyester resins, however, could not be used as a packaging material for high gas barrier property, since gas permeability thereof is so high against such gas as oxygen.
Polycarbonates, too, could not be used as a packaging material for which a high gas barrier property is required, such as for foodstuff, since gas permeability thereof is so high against such gas as oxygen, although they are excellent in transparency, heat resistance, and organoleptic property.
To increase the gas barrier property of polyethylene terephthalate resin or polycarbonate resin, there have been proposed methods to laminate the polyethylene terephthalate resin or polycarbonate resin with a resin having superior gas barrier property to said resins, such as saponified ethylene-vinyl acetate copolymers. However, the adhesive strength between the polyethylene terephthalate resin or polycarbonate resin and the saponified ethylene-vinyl acetate copolymer is not sufficient, and there are drawbacks such that partial delamination occurs during the lamination stage or service to deteriorate the gas barrier property or impair the appearance or mechanical strength of the prepared product.
To overcome such drawbacks, for example, Japanese Laid-open Application No. 61-270155 and Japanese Laid-open Application No. 62-158043 disclose a laminated material comprising a polycarbonate layer or a polyester layer and a saponified ethylene-vinyl acetate copolymer layer which are bonded to each other with an intermediate layer consisting of a graft copolymerized ethylene/.alpha.-olefin random copolymer grafted with an unsaturated carboxylic acid or its derivative. Although such laminated material has excellent adhesive property at ordinary temperatures as well as excellent gas barrier property, there have still remained problems such that the adhesivity of the laminated material often deteriorates with heat when it undergoes heat treatment such as high temperature packing or treatment in retort, thus causing delamination of the bonded layers with the result that the gas barrier property is impaired.
Furthermore, there is disclosed in Japanese Patent Application No. 64-45445, which pertains to the present inventors, an adhesive resin composition having a graft ratio between 0.01 and 3 weight % for the composition as a whole, a melt flow rate between 0.1 and 50 g/10 minutes and a degree of crystallinity of less than 35%, comprising (a) 95 to 50 weight % of an ethylene/.alpha.-olefin copolymer having a melt flow rate between 0.1 and 50 g/10 minutes, a density between 0.850 and 0.900 g/cm.sup.3, an ethylene content between 75 and 95 mole %, and a degree of crystallinity by X-ray diffraction of less than 30%, (b) 5 to 50 weight % of an ethylene-vinyl acetate copolymer having a melt flow rate between 0.1 and 50 g/10 minutes, and a vinyl acetate content between 5 and 40 weight %, and (c) a graft copolymerized polypropylene grafted particially or totally with 0.05 to 15 weight % of an unsaturated carboxylic acid or its derivatives having a melt flow rate between 0.1 and 50 g/10 minutes, a density between 0.900 and 0.980 g/cm.sup.3, and a degree of crystallinity by X-ray diffraction of 30% or higher, said graft copolymerized polyethylene being contained at a ratio between 1.0 and 30 weight % of the total weight of the aforementioned (a) and (b), wherein said adhesive resin composition does not deteriorate its adhesivity between layers of a laminated material even after high temperature treatment such as high temperature packing or treatment in retort; and a laminated material constructed of a polyester layer or a polycarbonate layer, an intermediate layer consisting of said adhesive resin composition and a saponified olefin-vinyl acetate copolymer layer.
Although, the aforementioned adhesive resin composition maintains excellent adhesive property at ordinary temperatures after high temperature treatment, it has caused at times delamination in the aforementioned laminated material during high temperature packing or treatment in retort.
Thus, it has been desired to develop an adhesive resin composition which can completely prevent the laminated material from delamination even during high temperature packing or treatment in retort.